SECTION B
9 (a) What is meant by the term herbicides?
chemicals used to kill weeds/inhibit weed growth;
[1]
(b)Outline the difference between selective herbicides and non selective herbicides giving appropriate
examples if each
Selective herbicides
Kill certain weeds/plants
Used as post emergent
Absorbed by foliage/roots and translocated to
other parts of the plant
Dalapon/2, 4 D/ Simazine/atrazine; glyphosate/
other named appropriate selective herbicides
Non selective herbicides
Kill all weeds/plants;
Used as pre emergent ;
Absorbed by living tissues on a plant and they do not
move throughout the plant tissues;
Paraquat/bromaci/atrazine/simazine/other named
appropriate non selective herbicides
[4]
(c)Outline the advantages of using herbicides over the other available methods of weed control
quick/fast ; effective in controlling weeds within the rows; can be used even before the weeds set/ appear;
can be used in areas where other methods are practically impossible ; conserves soil moisture by minimizing
soil tillage ; guarantees almost complete control ; maintains good soil structure by minimizing soil tillage;
[max 5]
10 (a) What is meant by the term plant disease?
harmful/deviant condition caused by plant pathogens/deviation from normal functioning of a plant ;
[1]
(b)Describe the mode of infection for each of the following groups of diseases:
(i)bacterial disease
bacteria may be carried by wind/irrigation water/insects/crop residues/ implements/tools/soil ; enters
plants wounds/cuts;
[2]
(ii)fungal disease
spores may be carried by winds/irrigation water/insects/on seeds/crop residues/implements/tools; spores
germinates when landing on wet leaves; young fungi enters healthy plants through the stomata;
[max 2]
(iii)viral disease
viruses is carried by sap – sucking leaf hoppers/insects; the virus is injected/released into a sap of a
healthy plant when the insect/sap sucking leafhopper sucks the sap/AW;
[2]
c)Outline necessary precautions taken to ensure safe and effective use of chemicals in the control of plant
diseases
application at recommended rate; wear protective clothing; read/follow instructions; spraying in calm
weather/avoid spraying when it is windy/rainy; alert your neighbours of your intentions to spray; avoid
eating/smoking/drinking while handling chemicals; wash hands thoroughly /with detergent after using
chemicals; do not allow anybody to enters sprayed area until the required period expires;
[max 3]
11 (a) outline reasons for stumping in a field
to facilitate tillage operations/enables movement of machinery; to control pests/diseases; prevents
competition for space/nutrients/ sunlight/water; to prevent damage to implements/tools/machines; to
create space for crops/plants; to prevent injury/injury to farmers/animals;
[max 4]
(b)Explain how the following tillage operations contribute to soil preparation:
(i)ploughing
loosens the soil improving aeration/ infiltration/ drainage/ root development; inverts the soil which buries
organic matter/ weeds/ unwanted material/ expose pests/pathogens; break hard pans improving
aeration/infiltration/drainage/ water holding capacity ;
[max 2]
(ii) discing
cuts surface trash hence killing weeds; breaks surface crusts improving drainage/aeration ; breaks big soil
clods to cover seeds/level the soil/produce medium tilth;
[max 2]
(iii)harrowing
breaks clots producing fine/suitable tilth; levels the soil producing uniform depth of planting/ uniform water
distribution
[2]
12 (a)Describe how plants leaves manufacture food
have chloroplasts where photosynthesis takes place; chlorophyll/green pigment absorbs light/energy from
sunlight; light/sunlight /sunlight energy splits water molecules into hydrogen and oxygen atoms; carbon
dioxide is absorbed through the stomata of the leaves; carbon dioxide diffuses from the air spaces of the leaf
into the cytoplasm; water passes from the xylem tissues into the cells; carbon doxide combines with water to
form carbohydrates and oxygen/hydrogen combines with carbon dioxide to produce carbohydrates/ correct
word equation/ balanced chemical equation ; oxygen is released as a byproduct;
[max 5]
(b)Outline how food manufactured in plant leaves is utilized
used for plant growth/development/replacement of worn out tissues/maintenance; used for reproduction/
formation of flowers/fruits/seeds; improve quality of fruits; seeds/fruit ripening; used for seed germination;
essential to drive metabolic process/respiration; essential for nutrient absorption/active transport; develop
plant resistance against pests/diseases; stored for future use;
[max 5]
13 Paddocks can be become dominated by less palatable and low producing pasture plants
(a) Outline factors that might cause the development of less palatable and low producing pasture plants
selective grazing; uncontrolled burning/veld fires; continuous grazing/not having enough rest periods;
overstocking/overgrazing; failure to control weeds/bush encroachment; drought/periodic droughts; uneven
distribution of water points/ poor water reticulation /use of the same pathways; mismatch between livestock
type and available forage/AW;
[max 5]
(b)State what can be done to improve the condition of the pasture
apply non selective grazing/control selective grazing; give the camp ample opportunity to rest; apply
fertilizers; irrigation; put enough livestock on the land/balance stocking rate with carrying capacity/
practice correct stocking rate; reseeding with desirable species; practice supplementary feeding; match
livestock type with available forage; practice rotational grazing; distribution of watering points; controlled
burning;
[max 5]
14. Explain each of the following economic concepts using relevant illustrations :
(a) the law of demand
The higher the price of a commodity, the lower the demand/ AW;
[1]
Price
60
Quantity
250
40
20
500
1000
Correct sketch of demand curve/demand schedule;
Correct labeling of Y – axis/ column 1;
Correct labeling of X-axis/ column 2;
[max 2 ]
Correct interpretation of law of demand/when the price of oranges per bag increased from P1/P20 to P2/P60
the quantity of oranges demanded decreased from Q1/1000 bags to Q2/250 bags/AW;
[2]
(b) equilibrium price
Price that satisfy both the producer and consumer/price at which amount supplied is the amount
demanded/AW;
[1]
Price
8
6
4
Demand
30
40
50
Supply
50
40
30
Correct sketch of equilibrium price;
Correct labeling of supply curve and demand curve;
Correct labeling of Y-axis/column 1;
Correct labeling of X- axis/ column 2;
Correct labeling of equilibrium price;
[max 2 ]
Correct interpretation of equilibrium price/ at equilibrium price P/6 the quantity of tomatoes demanded was
equal to the quantity of tomatoes supplied that is 40/Quantity supplied/quantity demanded / AW;
[2]
15. (a) Describe the dangers of operating a tractor without lubrication
increased friction between moving parts; reduced efficiency; overheating of the engine; increased noise
between moving parts/in the engine;
[4]
(b) Outline the differences and similarities between the mode of operation of a 4-stroke petrol engine and a
diesel engine
Differences
Phases
Petrol
Diesel
Induction
Fuel-air mixture drawn into the
cylinder
Only air is drawn into cylinder
Compression
Fuel-air mixture is compressed
Air is compressed
Power
Electric spark ignites fuel mixture
Hot air/compressed air ignites the fuel/diesel
[3]
Similarities
Stage
Petrol
Diesel
Exhaust
Burnt gases are swept out through the
exhaust port
Burnt gases are swept out through the
exhaust valve
Inlet valve closed and exhaust valve open
Inlet valve open and exhaust valve open
Piston moves up
Piston moves up
Inlet valve open and exhaust valve closed
Inlet valve open and exhaust valve closed
Piston moves down
Piston moves down
Both inlet and exhaust valves closed
Both inlet and exhaust valves closed
Piston moves up
Piston moves up
Both inlet and exhaust valves closed
Both inlet and exhaust valves closed
Piston moves down
Piston moves down
Induction
Compression
Power
[3]